1. Field of the Invention
The present invention relates to a planar illumination device.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2008-218218 discloses a planar illumination device. In the planar illumination device, an easy folding line such as a slit is formed on a circuit board mounted with an LED so that a portion where the LED is not mounted is folded with respect to a portion where the LED is mounted, and the circuit board is folded and mounted on a frame, to thereby achieve reduction in thickness of the planer illumination device even if the circuit board having a width greater than a height dimension of the LED is used.
In this planar illumination device of Japanese Patent Application Laid-open No. 2008-218218, the folded portion of the circuit board is laid along a bottom surface of the frame, and a back surface of the mounted portion of the circuit board where the LED is mounted is fixed and adhered by a double coated adhesive tape onto a side wall surface of the frame.
Since restoring force for the folded portion to return to a state before the folding is small due to the formation of the easy folding line, force causing the double coated adhesive tape to peel off is difficult to work thereon, and since the mounted portion is able to be adhered closely to the frame, effect of radiating heat generated by the LED to the frame is increased, and thus the fixing thereof is able to be achieved securely over a long period of time.
However, just by the formation of the easy folding line through provision of the slit, under a harsh environment, such as under high temperature and high humidity, there is still concern over fluctuation and deterioration of illumination characteristics due to the circuit board (mounted portion) peeling off the frame.